The physicochemical properties of graphene and other two-dimensional nanomaterials, including the electronic structure, chemical activity and mechanical strength of the materials, are crucially dependent on the edge geometries, grain boundaries and relative crystallographic orientation of the individual constituent single crystal domains. Hence, for the successful implementation of graphene as transparent conducting electrodes or in sensor and nanoelectronic device applications, the generation of graphene with predefined edge geometries and orientation is of essential importance. Despite tremendous efforts, to date the tailored manufacturing of graphene by CVD with controlled domain orientation and defined edge geometries remains unsolved.
Hexagonally shaped graphene domains with defined zigzag edges have been synthesised through atmospheric-pressure CVD (APCVD) (see Yu et al, Nat. Mater. 10, 443-449, 2011; and Luo et al, ACS Nano 5, 9154-9160, 2011). However, these domains are randomly oriented on the substrate, resulting in a mismatch between the relative edge geometry of neighbouring domains. As the individual domains grow and coalesce, structural defects will inevitably be introduced into the film that will degrade the properties of large-area films (see Tapaszto et al, Appl. Phys. Lett. 100, 053114, 2012; and Banhart et al, ACS Nano 5, 26-41, 2011). Moreover, no correlation has been identified between the crystallographic orientation of the graphene network and that of the underlying copper grains. Indeed, some publications suggest that only a weak interaction exists between the copper and graphene (see Yu et al supra; and Rasool et al, Nano Lett. 11, 251-256, 2011). The lack of alignment of graphene domains within a single copper grain, and the invariant shape of domains growing across copper grain boundaries, has led some to suggest that no epitaxial relationship exists between the substrate and graphene layer.
There remains a need in the art for improved processes for the production of two-dimensional nanomaterials, in particular graphene.